1. Field of the Invention
The present invention is directed to nitrogen generators, and in particular, portable cryogenic nitrogen generators.
2. Description of the Related Art
Inert gases are widely used in many industrial processes. For example, nitrogen gas is commonly used in conjunction with operation of a drilling rig for oil, gas, or geothermal wells, as well as for post drilling operations. In particular, nitrogen is injected into the down-hole region during a drilling operation, to remove drill cuttings.
In the art of well drilling, tubular casings are typically inserted into the wells so as to secure the perimeter of the wellbore. In some wells, multiple casings are secured at the surface of the well to lower down-hole locations. Other types of casings, called liners, are sometimes used to extend from the lower-most casing into the lower-most portion of the wellbore. Drilling fluids, such as drilling mud, are often used when large flows of water are present in the well. The drilling mud is circulated down the drill string, through the drill bit, and up the annular region between the drill string and the wellbore or casing. Gas, such as Nitrogen gas, may be injected into the down-hole region to provide faster drilling when substantial amounts of water are not present in the well.
In the past, air has been used as the principal down-hole drilling fluid for lower water content drilling. The air can be combined with a surfactant, foaming agent, water, and/or mud for different applications. The primary advantages of straight air drilling are greatly increased penetration rates, greater bit footage, and fewer down-hole drilling problems.
However, drilling with air does raise a number of disadvantages. For example, injection of high-pressure air into a down-hole during a drilling operation increases corrosion rates and raises the risk of explosions or fire due to the presence of high levels of oxygen in the pressurized air. In order to reduce the risk of explosions or fire, it has been known to reduce the temperature of the injected air, or to replace the air with an inert gas, such as Nitrogen.
One option for supplying nitrogen gas to the down-hole region of a well during a drilling operation is to ship containerized nitrogen to the drilling site and pump the nitrogen gas into the well at a pressure from about 200 psig to 10,000 psig. However, the shipment of containerized nitrogen to a drilling site, which may be in a remote location, can be expensive. Thus, it is more desirable to generate nitrogen gas at the site of the drilling operation.
One option for producing nitrogen gas at a drilling site is disclosed in U.S. Pat. No. 6,041,873 issued to Michael, the entire contents of which is hereby expressly incorporated by reference. The Michael patent discloses a portable unit that produces nitrogen gas through non-cryogenic systems including membrane separation units.